Glycol regeneration using eductor flash separation

ABSTRACT

Reconcentration of liquid desiccant, such as glycol, used in the dehydration of gaseous steams, is accomplished by aiding the separation of water subsequent the reboiler by an induced vacuum into a separate flash chamber. The vacuum is created by a pump that is fluid impelled by either the desiccant or gas available in the process.

Unite States Fatet Gravis, llllll et all.

[ Mar. M, 11972 GLYCOL REGENERATION USING EDUCTOR FLASH SEPARATIONCharles K. Gravis, Ill; Harold S. Wood; Robert A. Hodgson, all of Tulsa,Okla.

Maloney-Crawford Tank Corporation, Tulsa, Okla.

Feb. 27, 1969 [72] Inventors:

[73] Assignee:

Filed:

Appl. No.:

U.S.Cl ..55/32,55/169, 55/195 Int. Cl ..B0ld 53/14 Field of Search..55/32, 40, 41, 42, 44, 49,

References Cited UNITED STATES PATENTS Glasgow et al 53 22 GLYCOLREBOILER 3,217,466 11/1965 Bogart ..55/44 3,318,071 5/1967 Sinex...55/32 3,347,019 10/1967 Bamhart ..55/32 3,370,636 2/1968 Francis, Jr.et a1. ..55/32 3,397,731 8/1968 Gravis et al. ..55/32 X 3,451,897 6/1969Welch ..55/32 X Primary Examiner-Charles N. Hart Attorney-Head andJohnson [57] ABSTRACT Reconcentration of liquid desiccant, such asglycol, used in the dehydration of gaseous steams, is accomplished byaiding the separation of water subsequent the reboiler by an inducedvacuum into a separate flash chamber. The vacuum is created by a pumpthat is fluid impelled by either the desiccant or gas available in theprocess.

13 Claims, 3 Drawing Figures mmnm GLYCOL ACCUMULATOR a AAA/(AAA K vvvvvI;

LEAN GLYCOL TO PUMP SUCTION RICH GLYCOL FROM CONTACTOR PAIENTEDMAR 14I972 SHEET 1 BF 3 mOFOaFZOQ 20mm JOO J0 IQE CHARLES K. GRAVIS HAROLD BYROBERT m 3. W000 A. HODGSON ATTORNEYS PAIENTEDMAR 14 I972 3, 6A8 A34SHEET 2 UF 3 R O 4 l 3 2 :3 U 0 1:

I O O 5 (D UJ g 5 A I U) 3 LL rd w o R131 ch Q l) M OD: g 35l/VVE/VTORS. -50: CHARLES K.GRAVIS, In R g HAROLD s. WOOD 9 2m By ROBERTA. HODGSON 0 w Pm R i ATTORNEYS GLYCOL REGENERATION USING EDUCTOR FLASHSEPARATION BACKGROUND OF THE INVENTION Liquid desiccants, such asglycols, are quite extensively used in the dehydration of natural gasstreams. A typical separation process includes a contacting tower inwhich the liquid desiccant is brought into intimate contact with thenatural gas stream to be dehydrated. The glycol becomes enriched by thewater, is removed, and is then reconcentrated, usually by boiling offthe water with heat. The reconcentrated desiccant is then recirculatedeither to an accumulation point or to the contacting vessel.

Because of the upper limits to which liquid desiccant can be subjectedto heat, the reboiling procedure alone does not remove all of the waterfrom the desiccant. Reboiler heat processes typically can reconcentratethe glycol to a little over 98.5 percent by weight when operated at atemperature of about 380 F. A one-tenth of one percent gain inreconcentration provides an even greater gain in dew point depression ofthe gas being dehydrated. Others, such as shown in US Pat. No.3,370,636, have attempted to shift the vapor equilibrium of theheat-reconcentrated desiccant by developing a vacuum using a steam jetabove the surface of the reboiler. The desiccant is caused to flow fromone chamber to another by the induced vacuum. Placing steam into theprocess merely adds additional water to the system if recycled to thereboiler, yet will waste glycol if vented. Additionally, such a systemis merely an adjunct to the reboiler heat system and does not utilizeavailable and waste energy to create the vacuum.

SUMMARY OF THE INVENTION Accordingly, this invention provides a flashchamber separated from the desiccant reboiler, within which preheatedpartially reconcentrated desiccant such as glycol, is subjected to avacuum from a fluid-impelled pump such as a jet type eductor. Theeductor is driven by fluids used in the process such as rich glycol froma dehydration contactor on its way to the reboiler. Another embodimentproposes using dry gas as the eduction medium. A yet additionalembodiment uses the eductor in combination with a reboiler heatgenerated diffusion pump to create even higher vacuum in the flashchamber than can be obtained by the eductor alone.

In the process provided by this invention the total fluid stream to betreated is first removed under vacuum conditions from the reboiler wheresome flashing of vapor and cooling occur. This fluid is then preheatedby a reboiler heat exchanger, then subjected to the flash separation ina separate treating vessel where the vacuum is induced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a typical embodiment of thisinvention wherein rich glycol is used as the educting medium forcreating a vacuum within a glycol flash chamber.

FIG. 2 is an alternate embodiment of this invention utilizing gas as theeducting medium for creating a vacuum and increasing the concentrationof glycol.

FIG. 3 is an additional embodiment using an eductor, driven by richglycol from the contactor, in combination with a reboiler heat generateddiffusion pump in creating even lower vacuum in the flash chamberseparated from the reboiler.

DESCRIPTION OF THE PREFERRED EMBODIMENT Before explaining the presentinvention in greater detail, it is to be understood that the inventionis not limited in its application to the details of construction and thearrangement in parts illustrated in the accompanying drawings, since theinvention is capable of other embodiments and of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation.

Referring now to FIG. I, glycol, rich in water received from a gasdehydration contactor tower, not shown, is caused to pass throughconduit It) to a sump tank 111. Gas separating therefrom is used asneeded through pipe 13, by the reboiler burner as fuel, controlled byvalve 15 or is vented. The glycol outlet of tank 11 passes to theaccumulator coil 12 where the glycol is heat exchanged withreconcentrated glycol within the vessel. The outlet 14 therefrom iscaused to be injected into an eductor 16 which by the jet or venturiaction creates a low pressure which pumps fluids through heat exchangerconduit 18 into the eductor where both are caused to flow throughconduit 20 into the stripping column 22 of glycol reboiler 24. Asubmerged heater tube 26 and its internal burner are mounted in thereboiler as a primary means to boil off a large percentage of the waterwhich the glycol has absorbed from the contacting tower. Vaporstherefrom are withdrawn through stripping column 22 and out throughconduit 44. Partially reconcentrated glycol passes from the reboilerthrough a conduit 28 into a float operated trap 30 by which the levelwithin the reboiler is maintained substantially constant. Communicationis made between the trap and the upper portion of the reboiler byconduit 32 to equalize pressure. The partially reconcentrated glycol, inthis embodiment, is withdrawn from trap 30 and caused to pass and returninto the reboiler 24 where it is heat exchanged with the glycol thereinthrough coil conduit 34, the outlet of which enters the vacuum flashseparator chamber 36. The chamber 36, like most of the related conduitand equipment, is preferably insulated and may be packed as for examplewith Beryl saddles or other packing. The upper part of the chamberconnects with conduit 18 on the vacuum side of the eductor after passingthrough a natural draft condenser 38 which further aids the vacuumcreation. Flash vapor from chamber 36 passes through natural draftcondenser 38 where most of the water and glycol in the vapor arecondensed. The mixture of condensate and noncondensibles (including anyair leakage) is exhausted through conduit 18 into the low pressure portof eductor 16. Maximum condensation of this stream is important toachieve maximum vacuum with the eductor. It is to be understood thatother heat exchange means may be used as are [known in the art. Thehigher reconcentrated glycol passes from the bottom of flash separator36 through conduit 40 into the glycol accumulator and thence intoconduit 42 to the pump suction which is supplying lean glycol to thecontacting tower and the cycle is repeated.

It is well to note that as the partially reconcentrated glycol passesthrough valve 30 some flashing and cooling occurs. Therefore animportant aspect of this invention is that before final flashseparation, the total glycol stream is reheated to substantially themaximum reboiler temperature.

The embodiment of FIG. 2 shows a contacting tower 50 wherein wet gasentering through conduit 52 into the lower portion of the vessel 50passes upwardly countercurrent to lean glycol which is entering throughconduit 54 after being heat exchanged at 56 with the dry gas streamleaving the contactor through conduit 58. Water-rich glycol or otherdesiccant leaves the contactor through conduit 60 at the lower portionthereof and by pump 62 is caused to travel to a sump, not shown but asin FIG. 1, through glycol accumulator coil 95 where it passes in heatexchange with lean glycol. From the accumulator, through conduit 66, theglycol enters stripping tower 68 of the glycol reboiler 70.Alternatively, part or all of the rich glycol may be caused to passthrough conduit 67 into heat exchange with the vapors leaving strippingcolumn 63 where they are returned through conduit 69 to the accumulatorheat exchange. A typical U-tube and burner 72 is provided to boil off alarge percentage of the water within the glycol desiccant, said watervapor and other entrained stripping gas leaving the stripping column 68through conduit 74. Partially reconcentrated glycol then passes to afloat operated trap 78 for maintaining the level of glycol within thereboiler. Partially reconcentrated glycol leaves the float trap 78through conduit 80 into insulated vacuum flash chamber 82 where it flowsthrough packing 84 which provides added surface to enhance theattainment of vapor-liquid equilibrium, thence outward through conduit86 into the glycol accumulator 64. Some communication is maintained fromthe top of the accumulator into the vacuum flash chamber by way ofconduit 88. A vacuum is maintained within the flash chamber by passingpressure gas, such as dry gas from conduit 58, through the conduit 90.This action through the eductorcreates a vacuum through conduit 92 intothe top of the flash chamber further aiding in the separation of vaporsfrom the partially reconcentrated glycol. In this embodiment theresultant gases may be recirculated through conduit 94 back into theglycol reboiler as a contacting medium with the glycol therein.

. Referring to the embodiment of FIG. 3, rich glycol from the contactorenters conduit 100 into heat exchange with the lean glycol inaccumulator 102. The outlet therefrom, under pressure, is caused to passthrough an eductor 104, the vacuum intake 106 of which is connected to adiffusion pump system 107 interconnected with the reboiler 108. Thediffusion pump in turn is connected through a natural draft heatexchanger 110 with the upper portion of an insulated flash chamber 112having packing 114 therein.

A float control outlet 116 from the reboiler passes partiallyreconcentrated glycol or other desiccant into heat exchange with thereboiler glycol through conduit 118 where it is caused to enter theflash chamber 112. The use of a diffuser pump of a type such asmanufactured by Central Scientific Company includes a heat pipe 120which is interconnected with the hot glycol within the reboiler. Vaporspassing upwardly are diverted by the baffles 122 through constructionswhich create additional vacuum. The combination of the eductor 104 andthe diffusion pump greatly increases the vacuum capable of being appliedto the partially reconcentrated glycol entering the flash chamber 112.

What is claimed:

1. A method of reconcentrating liquid desiccant used in a fluiddehydration contactor comprising:

partially reconcentrating said desiccant utilizing heat in a reboiler;controllably trapping and removing a separate stream of said partiallyreconcentrated desiccant from said reboiler;

conveying said stream to a flash chamber via a conduit which is in heatexchange with the desiccant adjacent the source of said heat in saidreboiler;

inducing a vacuum in said flash chamber to further reconcentrate saiddesiccant stream; and

removing said further reconcentrated desiccant stream from said flashchamber for use in said dehydration contactor.

2. A method according to claim 1 including creating said vacuum by afluid-impellent pump.

3. A method according to claim 2 wherein said fluid impellent is saidliquid desiccant from said contactor.

4. A method according to claim 3 wherein said impellent is heatexchanged with reconcentrated desiccant.

5. A method according to claim 2 wherein said fluid impellent isrelatively dry fluid from said contactor.

6. A method according to claim 5 wherein said fluid is a gas.

7. Apparatus for reconcentrating liquid desiccant used in a fluiddehydration contactor, such as glycol, comprising in combination:

a reboiler to create partially reconcentrated desiccant;

a float operated valve to trap and remove a portion of said partiallyreconcentrated desiccant and to maintain a substantially constant levelof desiccant within said reboiler;

a flash separation chamber separated from said reboiler;

conduit means to convey said portion of said partially reconcentrateddesiccant from the outlet of said float operated valve thence back intosaid reboiler adjacent the source of heat for heat exchange with theremaining partially reconcentrated desiccant therein, thence to saidflash chamber to make a higher reconcentrated desiccant;

means to induce a vacuum in said flash chamber; and means to flow saidhigher reconcentrated desiccant from said flash chamber to, eventually,said gas dehydration contacting tower.

8. Apparatus of claim 7 wherein said means to induce said vacuumcomprises a fluid impellent pump and vacuum conduit means connectingbetween said pump and said flash chamber.

9. Apparatus of claim 8 wherein said fluid impellent is liquid desiccantfrom said contactor.

10. Apparatus of claim 9 wherein said fluid impellent is heat exchangedwith said higher reconcentrated desiccant prior to use in said pump, andmeans to cool said vacuum conduit means.

11. Apparatus of claim 10 wherein a diffusion pump, using a heat sourcefrom said reboiler, is interposed in said vacuum line between saidchamber and said pump.

12. Apparatus according to claim 8 wherein said fluid impellent isrelatively dry fluid from said contactor.

13. Apparatus of claim 8 including means to cool said vacuum conduit.

2. A method according to claim 1 including creating said vacuum by afluid-impellent pump.
 3. A method according to claim 2 wherein saidfluid impellent is Said liquid desiccant from said contactor.
 4. Amethod according to claim 3 wherein said impellent is heat exchangedwith reconcentrated desiccant.
 5. A method according to claim 2 whereinsaid fluid impellent is relatively dry fluid from said contactor.
 6. Amethod according to claim 5 wherein said fluid is a gas.
 7. Apparatusfor reconcentrating liquid desiccant used in a fluid dehydrationcontactor, such as glycol, comprising in combination: a reboiler tocreate partially reconcentrated desiccant; a float operated valve totrap and remove a portion of said partially reconcentrated desiccant andto maintain a substantially constant level of desiccant within saidreboiler; a flash separation chamber separated from said reboiler;conduit means to convey said portion of said partially reconcentrateddesiccant from the outlet of said float operated valve thence back intosaid reboiler adjacent the source of heat for heat exchange with theremaining partially reconcentrated desiccant therein, thence to saidflash chamber to make a higher reconcentrated desiccant; means to inducea vacuum in said flash chamber; and means to flow said higherreconcentrated desiccant from said flash chamber to, eventually, saidgas dehydration contacting tower.
 8. Apparatus of claim 7 wherein saidmeans to induce said vacuum comprises a fluid impellent pump and vacuumconduit means connecting between said pump and said flash chamber. 9.Apparatus of claim 8 wherein said fluid impellent is liquid desiccantfrom said contactor.
 10. Apparatus of claim 9 wherein said fluidimpellent is heat exchanged with said higher reconcentrated desiccantprior to use in said pump, and means to cool said vacuum conduit means.11. Apparatus of claim 10 wherein a diffusion pump, using a heat sourcefrom said reboiler, is interposed in said vacuum line between saidchamber and said pump.
 12. Apparatus according to claim 8 wherein saidfluid impellent is relatively dry fluid from said contactor. 13.Apparatus of claim 8 including means to cool said vacuum conduit.